Add gene sets

[reedliu]

• GeneSetDB： https://genesetdb.auckland.ac.nz/gsdownload.php
  source db: https://genesetdb.auckland.ac.nz/sourcedb.html
• GeneSigDB： https://maayanlab.cloud/Harmonizome/dataset/GeneSigDB+Published+Gene+Signatures
• ToppCell Atlas: https://toppgene.cchmc.org/navigation/database.jsp
  https://toppcell.cchmc.org/biosystems/go/index3/COVID-19%20Atlas

Refer to: https://maayanlab.cloud/enrichr-kg/downloads